In Arizona v. United States, the Supreme Court unanimously agreed that the federal government has no basis to nullify the "show me your papers" provision of Arizona's immigration law. Conservatives Antonin Scalia and Clarence Thomas, moderate Anthony Kennedy, liberals Stephen Breyer and Ruth Bader Ginsburg -- even Obama appointee Sonia Sotomayor -- all shot down the administration's effort to stop that part of the law. (Obama appointee Elena Kagan stayed out of it because she had taken part in the action as a member of the administration.)

Yet even with that unanimity -- a position supported, if the polls are correct, by a solid majority of the public and an overwhelming majority of Republicans -- GOP presidential candidate Mitt Romney would not specifically say he agreed with the court's view on "show me your papers."

Shortly after the decision was released Monday, Romney released a statement accusing President Obama of failing to lead on immigration. Romney did not say anything explicitly about the ruling but added, "I believe that each state has the duty -- and the right -- to secure our borders and preserve the rule of law, particularly when the federal government has failed to meet its responsibilities." That suggested Romney approved of the "show me your papers" opinion, but just as clearly avoided saying anything specifically about it.

A few hours later, with Romney in Arizona for fundraising events, spokesman Rick Gorka met reporters on board the candidate's plane. What followed was an excruciating back-and-forth in which the reporters pressed Gorka to say whether Romney agreed or disagreed with the decision. Gorka wouldn't go along. "The governor believes the states have the rights to craft their own immigration laws, especially when the federal government has failed to do so," Gorka said. But did Romney have a specific reaction to the Arizona decision? The spokesman wouldn't say, no matter how many times the question was asked.

The Romney campaign was not taken by surprise by the ruling. It was widely expected that the court would release its Arizona opinion on Monday, and Romney just happened to be in Arizona, leading observers to figure he would have something definitive to say about the subject. Yet he did not.

In Romney's defense, Arizona v. United States was a difficult decision for both sides to digest, because it sent a profoundly mixed message. On the one hand, the court said clearly that the "show me your papers" provision can go into effect. If there is some sort of problem once it is in practice -- and there will inevitably be allegations of profiling -- then the courts can consider those. But for now, it's OK.

That is a big victory for the law's supporters and a big loss for the Obama administration. The president went to court to try to prevent the law -- and very specifically the "show me your papers" provision -- from taking effect, and he lost.

On the other hand, in striking down other provisions of the law, the court sent a clear message that states cannot pass their own immigration measures even if those measures do not conflict with federal law. "After this ruling, there is very little that states can do to try to make up for ineffective federal enforcement of immigration laws," says former Scalia clerk Ed Whelan. "While there was a lot of controversy over ['show me your papers'], it doesn't confer any authority the states didn't already have."

Later Monday, Romney addressed the Arizona decision in a slightly more substantive way. "I would have preferred to see the Supreme Court give more latitude to the states, not less," he said at a fundraiser in Phoenix. "And the states now under this decision have less authority, less latitude to enforce immigration laws."

Romney's words again suggested he agrees with the court's opinion on "show me your papers." But again, he offered nothing to make clear his position on the central issue of the Arizona immigration fight.

Perhaps Romney was just exercising his legendary caution. But if Scalia and Sotomayor can agree on something, what would be the risk in Romney agreeing with it, too?

Though it touched on many questions, the political fight over the Arizona immigration law focused on a very specific issue: Should police who have stopped a person for some legitimate reason then check that person's status if they have reason to believe he or she might be in the country illegally? On Monday, Mitt Romney had the perfect opportunity to align himself with the conservative -- and popular -- side of the question and declined to take it.

Byron York,The Examiner's chief political correspondent, can be contacted at byork@washingtonexaminer.com. His column appears on Tuesday and Friday, and his stories and blogposts appear on washingtonexaminer.com.